1. Field of the Invention
The present invention relates to a light scanning apparatus which deflects a light beam from deflection unit toward a object to be scanned using a reflecting member.
2. Description of the Related Art
In a light scanning apparatus used in an image forming apparatus such as a laser beam printer and a digital copying machine, a light beam which is emitted from light source means while optically modulated according to an image signal is periodically deflected by deflection unit such as a rotary polygon mirror. The light beam from the deflection unit is caused to converge in a spot shape on a object to be scanned such as a photosensitive drum and a photosensitive belt using an imaging optical element having an f-θ property, thereby forming a latent image.
Some of the pieces of light scanning apparatus have reflecting mirrors for folding the light beam in the apparatus in order to downsize the apparatus or to irradiate the object to be scanned with a light beam having a desired angle. The reflecting mirror for reflecting the light beam deflected by the deflection unit toward the object to be scanned is formed in a so-called long mirror. In such long reflecting mirrors, one of end sides in a longitudinal direction is supported by two points, and the other end side is supported by a single point, which secures flatness in disposing the long reflecting mirror in the light scanning apparatus. More specifically, generally each support position on the two-point support side is received away from each end portion in a crosswise direction of the mirror by a predetermined length, and the support position on the single-point support side is received in the substantially central portion in the crosswise direction of the mirror. There are also proposed a long reflecting mirror, wherein the support position on the single-point support side substantially coincides with one of the support positions on the two-point support side in the crosswise direction, and a long reflecting mirror, wherein the support position on the single-point support side is biased toward one side from the crosswise central portion of the mirror (see Japanese Patent Application Laid-Open (JP-A) No. 4-114121).
However, in the conventional support method, sometimes rotation vibration is generated about the support point particularly on the single-point support side due to vibration caused by a drive source of the image forming apparatus, which results in generation of a defective image (so-called uneven pitch).
In order to solve the problem, there is proposed a reflecting mirror which is bonded to a reflecting mirror retaining portion (see JP-A Nos. 6-337342 and 10-20628). In JP-A No. 6-337342, the reflecting mirror is retained in a side plate hole made in a mirror retaining side plate, a reflecting surface is supported by a projection formed in a part of the side plate hole, and the reflecting mirror is biased from the opposite side by an elastic member. At this point, a gap between the reflecting mirror and the projection of the side plate hole is bonded by a bonding agent, and a gap between the mirror and a portion where the mirror presses the side plate hole by gravity is also bonded by the bonding agent.
In JP-A No. 10-20628, an application thickness of the bonding agent is set smaller than a thickness of the reflecting mirror to consider a mirror angle variation caused by cure shrinkage in hardening the bonding agent. JP-A No. 10-20628 discloses a technique wherein an elastic member is used as means for suppressing the rotation vibration of the mirror instead of the bonding agent.
However, there are following problems in the conventional techniques.
In JP-A No. 10-20628, unfortunately surface accuracy of reflecting mirror is not improved because an end portion of the reflecting mirror is supported by surface contact with a mirror receiving portion. In JP-A No. 6-337342, because the mirror bonding surface and the bonding surface facing the mirror bonding surface are bonded by causing the bonding agent to flow between the mirror bonding surface and the bonding surface facing the mirror bonding surface, unfortunately the position of the mirror is easily displaced to generate the mirror angle variation due to the shrinkage in hardening the bonding agent.
Therefore, JP-A No. 2002-267984 discloses a configuration, wherein the reflecting mirror is fixed by the bonding agent while a mirror side face is received by a projection to suppress a decrease in positional accuracy of the mirror surface. However, depending on a material of the bonding agent, the bonding agent is deformed by receiving a force in a direction parallel to the mirror bonding surface by the rotation vibration of the mirror. Therefore, the vibration cannot be suppressed.